Arctic mammals wintered in darkness 53 million years ago

Washington, June 2 (ANI): A new study has suggested that ancestors of tapirs and ancient cousins of rhinos living above the Arctic Circle 53 million years ago endured six months of darkness each year in a far milder climate than today that featured lush, swampy forests.

According to University of Colorado (CU) Boulder Assistant Professor Jaelyn Eberle, the study shows several varieties of prehistoric mammals as heavy as 1,000 pounds each lived on what is today Ellesmere Island near Greenland on a summer diet of flowering plants, deciduous leaves and aquatic vegetation.

"But, in winter's twilight they apparently switched over to foods like twigs, leaf litter, evergreen needles and fungi," said Eberle.

The team used an analysis of carbon and oxygen isotopes extracted from the fossil teeth of three varieties of mammals from Ellesmere Island - a hippo-like, semi-aquatic creature known as Coryphodon, a second, smaller ancestor of today's tapirs and a third rhino-like mammal known as brontothere.

"Animal teeth are among the most valuable fossils in the high Arctic because they are extremely hard and better able to survive the harsh freeze-thaw cycles that occur each year," Eberle said.

Telltale isotopic signatures of carbon from enamel layers that form sequentially during tooth eruption allowed the team to pinpoint the types of plant materials consumed by the mammals as they ate their way across the landscape through the seasons, according to Eberle.

"We were able to use carbon signatures preserved in the tooth enamel to show that these mammals did not migrate or hibernate," she said. "Instead, they lived in the high Arctic all year long, munching on some unusual things during the dark winter months," she added.

"An analysis of oxygen isotopes from the fossil teeth helped determine seasonal changes in surface drinking water tied to precipitation and temperature, providing additional climate information," said Eberle.

The results point to warm, humid summers and mild winters in the high Arctic 53 million years ago, where temperatures probably ranged from just above freezing to near 70 degrees Fahrenheit.

The study has implications for the dispersal of early mammals across polar land bridges into North America and for modern mammals that likely will begin moving north if Earth's climate continues to warm. (ANI)